1. Field of the Invention
The present invention relates to satellite-borne visible scanners. More particularly, this invention relates to a device designed to continuously monitor the celestial sphere for near earth objects.
2. Description of the Related Art
The earth is continually bombarded by asteroids and comets, most of which are harmlessly burned in the atmosphere. However, a fraction of these objects do impact the earth's surface, as evidenced by the many craters found around the globe. Such collisions of planetary bodies with the earth have played an important role in the geological, biological and climatological development of the earth. Asteroid collisions may have had a significant impact on biological evolution as a result of mass extinctions brought on by global climate change.
The destructive power of asteroid collisions has also been demonstrated in modern times. The 1908 Tunguska meteorite, the 1947 Sikhote-Alin meteorite and the 1945 meteor explosion over the pacific ocean all released energies equivalent to small thermonuclear devices. A near hit of an asteroid with the earth in 1991 underscores the vulnerability of our planet to sudden devastation.
Over 200 Near Earth Asteroids (NEAs) have been discovered. The Aten and Apollo class asteroids have earth intersecting orbits. While NEAs are usually smaller than 5 kilometers in diameter, asteroids as small as 50 meters in diameter pose a potential threat for significant destruction should one collide with the earth. NEAs are believed to arise from the decay of cometary nuclei or from ejection from the main asteroid belt.
To better comprehend the nature and magnitude of risks associated with collisions of near earth asteroids (NEAs) with the earth, a full understanding of the population of near earth objects is needed. Continuously monitoring the celestial sphere to detect near earth objects would give new insight into the distribution of asteroid sizes and orbits and would lead to a better understanding of the population of near earth objects.
Currently, ground-based telescopes are used for detecting and monitoring NEAs and other near earth objects. However, ground-based monitoring and detection schemes suffer from several limitations. For example, small objects such as NEAs with diameters of 50 meters cannot be reliably detected using ground-based telescopes. The performance of ground-based systems is affected by factors such as the sun, atmospheric turbulence, and cloud cover which limit the size and distance of the NEAs detected. Additionally, there are only enough ground-based systems to monitor a small fraction of the celestial sphere every day. Because the earth turns on its axis with a twenty-four hour period, any ground based system can examine only one latitudinal section of the celestial sphere per day. Thus ground based systems are either inherently slow, or require an unacceptably large number of telescopes. The high cost of building the many needed observatories, the great number of persons needed to operate the systems, and the limiting factors of the sun, clouds and atmospheric turbulence make the use of ground-based systems prohibitive.